An injector of this type generally features an actuator that controls an injection valve. If the injection valve is opened by the actuator fuel is injected into a combustion chamber. For example the actuator operates a servo valve which in its turn hydraulically opens and closes the injection valve. The actuator can be activated electrically. For example the actuator consists of piezo-electric elements and expands when an electrical voltage is applied.
The structure of a typical injector is described on the basis of FIG. 1 that shows a cross section of a part of an injector with an actuator housing, a seal, a projection, a recess, an indentation, a support surface, a further indentation, a valve piston, a valve head, a control chamber and an injector housing. The actuator 10′ is normally located in an actuator housing 4′, whereas the injection valve (not shown) and/or the servo valve, typically comprising a valve piston 6′ and a valve head 7′, are located in an injector housing 1′. Valve head 7′ separates a control chamber 8′ from a return line 15′. The injector housing 1′ features an indentation 2′ into which a part of the actuator housing 4′ is inserted. Indentation 2′ of injector housing 1′ features a first bottom surface that is designed as a surrounding support surface 3′ for actuator housing 4′. In the middle of this indentation 2′ there is a further indentation 5′, in which the servo valve and/or the injection valve are located. After actuator housing 4′ is pushed into injector housing 1′, actuator 10′ can activate the valve assembly accommodated in further indentation 5′ that surrounds the servo valve and the injection valve. A longitudinal expansion of actuator 10′ pushes valve piston 6′ in the direction of valve head 7′ and lifts the latter up from its valve seat against the force of a spring 9′. The fall in pressure in control chamber 8′ causes hydraulic opening of the injection valve.
For precise setting of the idle stoke between actuator 10′ and the valve assembly there is a suitable adjustment shim E′ located on support surface 3′ of injector housing 1′.
So that fuel that is in the valve assembly cannot flow along the interfaces between the injector housing 1′ and the actuator housing 4′ a seal 13′ is provided between injector housing 1′ and actuator housing 4′. To this end, the actuator housing 4′ features a peripheral recess 11′ on its side surface, in which seal 13′, typically an O-ring seal, is located. Because of recess 11′, actuator housing 4′ features a projection 12′ that is oriented to the side.
The seal is stretched around the actuator housing. The actuator housing is then inserted into the injector housing. When this is done the seal rubs against the side walls of the indentation of the injector housing. This represents a particular disadvantage if the indentation is to be coated with a corrosion protection layer. It has become evident that the friction between the seal and the corrosion protection layer is so great that either the actuator housing cannot be inserted into the injector housing or the seal is destroyed when the actuator housing is pushed into the injector housing.